Best plural forms ranked:
1) internal (tours de force, culs-de-sac)
2) ending in -i (magi)
3) is to es (oases)
4) suppletive (people)
5) vowel changes (geese)
6) f to ves (thieves)
7) adding en (oxen)
8) no change (moose)
9) adding es, ies (boxes, babies)
10) adding s